U.S. Pat. No. 4,629,676 (Hayakawa et al.) and European Patent No. 0174634 (Fuji Photo Film Co., Ltd.) disclose an image forming method comprising the steps of imagewise exposing to light a light-sensitive material and heating the light-sensitive material. The light-sensitive material comprises a support and a light-sensitive hardening layer containing silver halide, a reducing agent and a polymerizable compound. The silver halide is developed by heating the light-sensitive material to form a polymer image. The polymerization is initiated by an oxidation radical of the reducing agent (including a radical formed from an oxidation product of the reducing agent).
U.S. Pat. No. 5,122,443 (Takeda), 5,290,659 (Takeda) and European Patent No. 0426192 (Fuji Photo Film Co., Ltd.) disclose embodiments of the light-sensitive materials, which are advantageously used for the preparation of a lithographic plate. In the light-sensitive materials for the lithographic plate, the light-sensitive hardening layer preferably comprises a hardening layer and a light-sensitive layer. The hardening layer contains a polymerizable compound or a cross-linkable polymer. The light-sensitive layer contains silver halide. The hardening layer or the light-sensitive layer further contains a reducing agent. The light-sensitive material can further comprise an over-coating layer provided on the light-sensitive layer.
A process for the preparation of a lithographic plate comprises the steps of imagewise exposing to light the light-sensitive material, heating the material, and removing the light-sensitive layer and the unhardened area of the hardening layer with an alkaline etching solution. The formed replica image is used as a printing plate.
The hardening reaction of the polymerizable compound or the cross-linkable polymer at the heat development is inhibited by oxygen in the air. U.S. Pat. No. 5,122,443 (Takeda), 5,290,659 (Takeda) and European Patent No. 0426192 (Fuji Photo Film Co., Ltd.) propose to use polyvinyl alcohol having a high saponification degree as a binder of the light-sensitive layer or the overcoating layer. The polyvinyl alcohol of the high saponification degree has a function of preventing oxygen from permeating into the hardening layer. The polyvinyl alcohol of the high saponification degree has another function of protecting components of the light-sensitive material (e.g., a reducing agent) from oxygen in the air while storing the material.